Writers in some fields summarize data by giving x¯ and its standard error rather than x¯ and sx. Biologists studying willow plants in Yellowstone National Park reported their results in a table with columns labeled x¯ ± SE The table entry for the heights of willow plants (in centimeters) in one region of the park was 61.55 ± 19.03. The researchers measured a total of 23 plants.

a. Find the sample standard deviation sx for these measurements.

b. A hasty reader believes that the interval given in the table is a 95% confidence interval for the mean height of willow plants in this region of the park. Find the actual confidence level for the given interval.